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Question

I will be using 12/3 Romex to make two separate circuits. As you know, 12/3 is 20 amp wire, for two separate circuits. There is a red wire (hot) for one circuit. There is a black wire (hot) for another circuit. There is a white wire (neutral) for both circuits. In other words, the black wire and the red wire both share the common white wire. Let’s say that one circuit draws 15 amps (red wire) and the second circuit draws another 15 amps (black wire). That is 30 amps. However, they both share the common white wire. The white wire is now carrying substantially in excess of 20 amps. In this case, it is carrying 30 amps and at full load from both circuits, it would have to carry 40 amps. Add it up. It means that the white wire is carrying the voltage from both individual 20 amp circuits (40 amps). The white wire would melt and catch fire instantly. Hence, 12/3 circuits and 12/3 Romex seem dangerous --- but they are used all the time. I don’t understand.
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Answer 1

Why did you ask the same question twice? See my answer to the other copy of this question.

Bottom line, a multiwire branch circuit when installed correctly will not overload the neutral. If you don't know how to install it correctly, get an electrician to do it.

Answer 2

If the circuit is perfectly balanced as you say, the neutral will be carrying 0 amps. The neutral only carrys the the unbalanced load. If one hot wire was pulling 10 amps and the other was pulling 7 amps the neutral will be carrying 3 amps. If properly installed there is no way that the neutral can become overloaded.

Answer 3

If such is the case.Then the red and black wires are different phases.Which means it will work but is not code.Why:: if your white wire (neutral)goes open between the box neu and the outlets you could have 220V at each plug (and smoke your equipment).The way to check is with a voltmeter between the hot side of the 2 outlets.Reason I say to check is that red is usually off a switch,which would mean you haven't traced the wires correctly.At any rate it should be brought up to code.Oh its 12-2 wg (12agw,2wires,with gnd)

Answer 4

The power coming into the breaker box is 220vac single phase. This is 2 legs of 120vac @ 60Hz. This means that it pulses 60 times a second per each leg and not at the same time. So the load of the wht wire carries the return @ 120hz. Three phase it would be @ 360hz . The point is as long as the double breaker is connected to the 2 legs, phase #1 (blk wire)and phase #2(red wire), the white is rated to carry both. http://en.wikipedia.org/wiki/Split_phase

Answer 5

not quite correct in ur thinking....ur assuming that the neutal will be carrying the full load, and even under the worst conditions if you have grounded correctly it wont. it would only carry the full load in a dead short condition.
go to ur panel and take a reading on any given #12 neutral....its a minimal reading.
you have to take into account the load on the other end, which i dont think you did

Answer 6

Don't forget the green wire for ground. But it shouldn't work but it does. Maybe someone really knows I don't